1. Field of the Invention
The present invention relates to a film coating unit and film coating method to form, for example, interlayer insulation film, insulation film as overcoat for device, and so on by applying predetermined coating liquid to a surface of a substrate such as a semiconductor wafer.
2. Description of the Related Art
As one of the semi-conductor manufacturing process, in order to form insulation film such as interlayer insulation film, for example, such technique is known that liquid film is prepared by applying coating solution on a surface of a substrate such as a semiconductor wafer wherein precursor material of silicon oxide film is dissolved in solvent and the solvent is vaporized from this liquid film to form the insulation film which is coating film comprising silicon oxide film.
As one of techniques for applying the coating solution on the surface of a substrate, such technique is known as to apply the coating solution in a manner of so-called drawing with one stroke drawing (for example, refer to Patent Document 1 and Patent Document 2).
With respect to coating techniques in a manner of this drawing with one stroke drawing, one example, will be briefly described taking a semiconductor wafer (herein after referred to as a wafer) as a substrate to be processed. As shown in FIG. 13, here, a wafer W is held on a substrate holder and a coating solution discharge nozzle 10 is disposed opposite to a surface of the wafer W. A small-diameter discharge orifice of the coating solution discharge nozzle 10 supplies coating solution 11 on the surface of the wafer W. The coating solution discharge nozzle 10 reciprocates in an X-direction and the wafer W is intermittently moved in a Y-direction while supplying the coating solution 11. In this case, it is desirable to cover by masking 12 a part aside from an area where circuit is formed on the wafer W to prevent that coating solution attaches to a rim and a back side of the wafer W. According to this technique, a coating film may be formed without wasting the coating solution as the wafer W is not rotated, for example, so as in a spin coating method. And, specifically, this coating method is preferable in case of coating a large sized substrate.
[Patent document 1] JP, A, No. 2002-353132
[Patent document 2] JP, B, 33-10788
However, in the above coating technique, it takes considerable time for the coating solution discharge nozzle 10 to move along a coating course from a front end to a terminal end of the wafer W to apply the coating solution entirely to the surface of the wafer W. So, solvent evaporates first from a part to which the coating solution is applied ahead, and the coating solution applied dries out or dehydrates. And due to evaporation of the solvent, surface tension of the coating solution applied is increased. Therefore, a problem that the coating solution which is applied later is pulled or drawn by the coating solution which is applied ahead, resulting that film thickness of the part to which the coating solution is applied ahead is enlarged.
One of counter measures to solve this problem is disclosed by Patent Document 1. Here, a top board (cover) is provided at predetermined height so as to cover a surface of the wafer W to control drying state of the coating solution. However, coating solution must be selected according to planned type of film. If coating solution of low viscosity, for example, to be selected for interlayer insulating film is processed in the same condition as in other coating solution of other high viscosity, drying state of the coating solution is not controlled sufficiently in some case. Thus, another coating unit should be considered.
And, Patent Document 2 discloses technique to control drying speed of a coating solution or a coating film by means of supplying solvent vapor thereto. According to the disclosure, a top board, which is disposed opposite to a surface of the wafer W, is provided with a plurality of perforations in a surface of the top board, and solvent vapor is supplied via the perforations to the coating solution or the coating film. However, if the solvent vapor or steam is sprayed via the perforations to the coating solution or the coating film on the surface of the wafer W, there is a concern that the air current disturbs surface of the coating solution or the coating film on the wafer W, resulting in uneven thickness of the coating solution or the coating film thereon.
The present invention was made based on such circumstances. It is an object of the present invention to provide a novel film coating unit and a novel film coating method to form an even coating film such as insulation film on or over a surface of a substrate by controlling drying state of the coating solution which is applied to the surface of the substrate in a direction from a front end toward a rear end thereof, for example, in a manner of so-called drawing with one stroke.